Creation and translation of low-relief texture for a photovoltaic cell

Abstract

Low-relief texture can be created by applying and firing frit paste on a silicon surface. Where frit contacts the surface at high temperature, it etches silicon, dissolving silicon in the softened glass frit. The result is a series of small, randomly located pits, which produce a near-Lambertian surface, suitable for use in a photovoltaic cell. This texturing method consumes little silicon, and is advantageously used in a photovoltaic cell in which a thin silicon lamina comprises the base region of the cell. When the lamina is formed by implanting ions in a donor wafer to form a cleave plane and cleaving the lamina from the donor wafer at the cleave plane, the ion implantation step will serve to translate texture formed at a first surface to the cleave plane, and thus to the second, opposing surface following cleaving. Low-relief texture formed by other methods can be translated from the first surface to the second surface in this way as well.

What is claimed is: 
     
       1. A method to form texture at a surface of a photovoltaic cell, the method comprising the steps of:
 applying a mixture containing glass frit to a first surface of a silicon body; 
 firing the glass frit mixture, wherein firing the glass frit mixture causes selective etching of silicon at the first surface; 
 removing all of the fired glass frit, leaving the first surface textured; and 
 fabricating the photovoltaic cell, wherein the photovoltaic cell comprises the textured first surface. 
 
     
     
       2. The method of  claim 1  wherein the glass frit is one or more of lead oxide glass, bismuth oxide glass, zinc oxide glass, aluminum oxide glass, cadmium oxide glass, magnesium oxide glass, borosilicate glass, calcium borosilicate glass, palladium oxide glass, barium borosilicate glass, or zirconium oxide glass. 
     
     
       3. The method of  claim 1  wherein the textured first surface has an average peak-to-valley height between about 50 nm and about 1 micron. 
     
     
       4. The method of  claim 1  wherein, at the textured first surface, the average pitch of the textured first surface is between about 0.5 microns and about 5 microns. 
     
     
       5. The method of  claim 1  wherein the silicon body is monocrystalline silicon. 
     
     
       6. The method of  claim 1  wherein, in the completed photovoltaic cell, the first surface is a surface of a silicon lamina having a thickness between about 1 microns and about 10 microns. 
     
     
       7. The method of  claim 6  further comprising, following the step of removing all of the fired glass frit, providing a receiver element adhered to the first surface with zero, one, or more layers intervening. 
     
     
       8. The method of  claim 6  further comprising, before the application of glass frit mixture, cleaving the silicon lamina from a silicon wafer, wherein the first surface is created during the cleaving step. 
     
     
       9. The method of  claim 1  wherein the silicon body is a lamina having a thickness less than about ten microns. 
     
     
       10. The method of  claim 1  wherein the step of applying a mixture of glass frit comprises applying the mixture of glass frit to at least 70 percent of the area of the first surface. 
     
     
       11. A method to texture opposing surfaces of a lamina, the method comprising the steps of:
 creating a first texture at a first surface of a donor body, wherein, for at least 50 percent of the area of the first surface, average peak-to-valley height is between about 100 nm and about 1500 nm, and average peak-to-peak distance is between about 140 nm and about 2100 nm; 
 implanting ions through the textured first surface, thereby defining a cleave plane within the donor body; and 
 cleaving the lamina from the donor body at the cleave plane, 
 wherein the first surface of the donor body is a first surface of the lamina, and 
 wherein a second surface of the lamina, the second surface opposite the first surface, is created by cleaving, and 
 wherein, immediately following the cleaving step, the second surface has a second texture, wherein for at least 50 percent of the area of the second surface, average peak-to-valley height is between about 100 nm and about 1500 nm, and average peak-to-peak distance is between about 140 nm and about 2100 nm; 
 wherein the step of creating texture at a first surface comprises applying a mixture containing glass frit to the first surface. 
 
     
     
       12. The method of  claim 11  wherein lamina thickness is between about 1 micron and about 10 microns. 
     
     
       13. The method of  claim 11  wherein, for at least 80 percent of the area of the first surface, average peak-to-valley height is between about 100 nm and about 1000 nm and average peak-to-peak distance is between about 140 nm and about 1400 nm. 
     
     
       14. The method of  claim 13  wherein the step of creating the first texture at the first surface comprises etching at the first surface with a selective etchant, wherein the selective etchant etches the ( 100 ) plane at a higher etch rate than the ( 111 ) plane. 
     
     
       15. The method of  claim 11  further comprising fabricating a photovoltaic cell, the photovoltaic cell comprising the lamina. 
     
     
       16. The method of  claim 15  wherein the lamina comprises a base of the photovoltaic cell. 
     
     
       17. The method of  claim 15  further comprising, between the implanting step and the cleaving step, providing a receiver element adhered to the first surface of the donor body with zero, one, or more layers intervening. 
     
     
       18. The method of  claim 17  wherein the step of providing a receiver element adhered to the first surface of the donor body with zero, one, or more layers intervening comprises applying a material or stack of materials to the first surface, or to a layer on or above the first surface, wherein the receiver element is formed from the material or stack of materials. 
     
     
       19. The method of  claim 18  wherein the receiver element has a final thickness of at least 50 microns. 
     
     
       20. The method of  claim 11  wherein, for at least 50 percent of the area of the first surface, average peak-to-valley height is between about 300 nm and about 1000 nm.